Intensification of the rate of diffusion controlled electrolytic oxidation of FeSO4 by turbulence promoters in a stirred tank reactor in relation to wastewater treatment

Abstract

The rate of diffusion controlled anodic oxidation of FeSO4 in rectangular stirred tank reactor was studied under galvanostatic conditions, H2 gas was produced as a byproduct at the cathode of the divided reactor. The rate of anodic oxidation of FeSO4 at a lead anode was enhanced by using active cylindrical turbulence promoters attached to the anode. Variables studied were impeller rotation speed, diameter and spacing of the turbulence promoters. The presence of turbulence promoters on the anode surface was found to increase the rate of FeSO4 oxidation by a factor ranging from 1.02 to 3.4 and reduce electrical energy consumption by an amount ranging from 25 to 80% depending on the operating conditions compared to the flat plate anode. The efficiency of the turbulence promoters was found to increase with increasing promoter spacing and diameter. The role of O2 bubbles which evolve at the anode surface simultaneously with FeSO4 oxidation in enhancing the rate of mass transfer jointly with turbulence promoters was discussed. Importance of the present study for treating wastewater containing FeSO4 was highlighted. Processes that produce wastewater containing FeSO4 include removal of H2S from petroleum hydrorefining gases by Fe2(SO4)3 oxidation to sulfur, regeneration of printed circuit etching solution and iron removal from steel mills pickling waste solutions. The importance of the present results in producing H2 at lower energy consumption and the possibility of integrating the present cell with the process of petroleum hydrorefining was noted. Also the importance of the present results in using FeSO4 as anodic depolarizer to reduce the cell voltage and energy consumption in the electrowinning of heavy metals from waste water was outlined.